The physics core is responsible for the maintenance of the positron emission tomograph (PET) and its associated computer systems, the development of image reconstruction, display and analysis software, and the development of methods to improve the quality and quantitative accuracy of the image data. The current tomograph is a General Electric Advance System. It includes 18 rings of detectors to produce 35 image planes. The tomograph data processing system utilize dedicated hardware for data acquisition and reconstruction (including a 20 cpu array for reconstruction). System control, image display, and all user interfaces are provided by two HP735 UNIX workstations. The facility includes a central DEC Alpha 2100/375 UNIX serve for software development and image processing. The tomograph provides a limiting resolution of 4 mm, a slice thickness of 5mm, and a sensitivity of 210 kcps/muCi/cc in 2D mode and 1160kcps/muci/cc in 3D mode. The machine can produce true coincidence count rates of greater than 600,000 events/second. The field of view if 50 cm with a patient tunnel diameter of 60 cm. The Core support is divided into two major sections: 1) those tasks that are unique to this P01 grant; and 2) those tasks that are common for all users of the PET facility. The majority of the Core support is of the second type and is provided through a cost center that has been set up to operate the PET system. All user of the PET facility are charged an hourly rate to support the costs of performing the scans, maintaining the tomograph, and implementing general improvements of the tomograph. Under the cost center approach, all users of the facility contribute equally to the costs of operation. Improvements under development include software tools to automate many aspects of quality assurance testing and normal tomograph operations (reducing the amount of imaging technician time required for non-scan activities). To increase the number of scans that can be done in the facility, considerable effort is underway to improve the quality of torso imaging in 3D mode. Improved scatter and attenuation correction techniques being developed under separately funded R01 grants will be implemented on the Advance system by the PET imaging cost center. In addition, techniques to reduce streak artifacts, alternative methods of image reconstruction to handle low count image sets, and improve methods to acquire attenuation data are all being developed by the cost center.